The hearing portion of the inner ear is enclosed within a hollow, spiral otic capsule bone shaped like a snail shell that is also referred to as the cochlea. The cochlea is a fluid-filled portion of the inner ear that contains nerve endings essential for hearing.
A biologically sealed attachment into the otic capsule bone that is stable and watertight is often desired for various medical devices and therapies. U.S. Pat. No. 5,951,601 (“the '601 patent”) and published United States Published Patent Application No. 2005/02033557 A1 (“the U.S. patent application”) both respectively describe procedures for attaching a therapeutic device, such as a microactuator, in a fenestration which pierces the otic capsule bone.
The inventions disclosed in the '601 patent and the U.S. patent application exhibit several advantages. A casing locates a therapeutic device very securely, without vibration. In addition, those inventions facilitate removing a therapeutic device if that were to become necessary. Thirdly, together with a precise atraumatic fenestration procedure the casing provides for a very precise location for a therapeutic device such as a microactuator. Thus, the casing ensures a microactuator or other therapeutic device is optimally situated in the cochlea without damaging the delicate structures of the inner ear.
The casings respectively disclosed in the '601 patent and the U.S. patent application are particularly adapted for implantation into a fenestration that pierces a projecting portion of the otic capsule bone called the promontory. As described in the '601 patent and the U.S. patent application, the casings are adapted for receiving and attaching to a subject a microactuator included in the implantable hearing aid system, a dummy plug to replace the microactuator should its removal become necessary, or any other type of therapeutic device that interacts with fluid or structures within the cochlea. If the casing receives a microactuator, applying an electric signal thereto causes the microactuator to directly stimulate fluid within the inner ear, which stimulation the subject perceives as sound.
A casing for attaching a therapeutic device to a fenestration formed through a subject's promontory in accordance with the respective disclosures of the '601 patent and of the U.S. patent application includes a sleeve having an outer surface. During implantation of the casing, a first end of the sleeve is received into the fenestration. Disposed in that location, the outer surface of the sleeve mates with the fenestration for securing the casing within the fenestration. The hollow sleeve includes an inner surface adapted to receive a barrel of the microactuator.
The casing also includes a flange that is integral with the sleeve. The flange projects outward from the outer surface of the sleeve about a second end of the sleeve that is located distal from the first end. The flange, through contact with the promontory, limits a depth to which the first end of the sleeve may enter into the fenestration.
A casing in accordance with the '601 patent or with the U.S. patent application may employ various means for securing the sleeve within the fenestration such as screwing into the promontory or clamping to the promontory. Similarly, such a casing may fasten the microactuator to the casing in various ways such as by a threaded attachment, with screws, with button-and-socket snap fasteners, or with a slotted tongue-and-groove lock. A casing in accordance with the '601 patent or the U.S. patent application may also include a keyway that receives a mating key formed on the barrel of the microactuator for establishing an orientation of the implanted microactuator.
One difficulty in a procedure for securing a therapeutic appliance into the otic capsule bone is that the attachment be biologically sealed. Another difficulty in a process for securing a biologically sealed therapeutic appliance to the cochlea is safely fenestrating the otic capsule bone, particularly the tiny promontory. For example, the maximum diameter of a fenestration piercing the otic capsule bone is approximately 1.0 to 1.5 mm. Furthermore, fenestrating the otic capsule bone must be accomplished without damaging the membranous labyrinth or organ of corti enclosed within the otic capsule bone, i.e. without damaging hearing.